With the development of science technology, the technology of electronic displaying upgrades steadily. Organic Light-Emitting Diode (OLED), as a new generation of display device, has the advantages of thin and light, high contrast, rapid response, etc, and is widely used in the electronic devices such as mobile phones, notebook computers, Wall-mounted television set, etc. OLED can be divided, according to its driving mode, into two types, i.e., Passive Matrix Driving OLED (PMOLED) and Active Matrix Driving OLED (AMOLED). The Active Matrix Driving mode has been widely used in the display for a large amount of information due to its capability of high display quality.
A traditional pixel unit driving circuit of AMOLED is shown in FIG. 1, and includes a switching transistor T, a driving transistor DTFT, OLED and a capacitor C. In FIG. 1, a gate of the switching transistor T is connected to a scanning line, a drain of the switching transistor T is connected to a data line, a source of the switching transistor T is connected to a gate of the driving transistor. A drain of the driving transistor DTFT is connected to a power supply VDD, a source of the driving transistor DTFT is connected to ground via OLED. The capacitor C is connected between the gate and the drain of the driving transistor DTFT. In this traditional pixel unit driving circuit, current flowing through OLED relates to the turn-on voltage Vth of the driving transistor DTFT.
AMOLED emits light due to a driving current generated by the driving transistor DTFT in a saturation stage. During the manufacturing procedure of Low Temperature Poly-silicon (LTPS), the evenness of the turn-on voltage Vth of the driving transistor DTFT is terribly bad and meanwhile the turn-on voltage Vth may drift. In the driving circuit shown in FIG. 1, different driving currents will be generated due to different turn-on voltages when the same voltage for a certain grey scale is input, which causes the inconsistency of the driving currents, that is, the unevenness of the current flowing through OLED and in turn the unevenness of the luminance of OLED.